Spiral fluted tap

ABSTRACT

As shown in FIG.  1 , rake surfaces of cutting edges  26  of a shank-side thread portion  24   b  formed in a full thread portion  24  are formed with chamfers  30  having the chamfer height Hmen fallen within the range of 15% to 100% of the thread height Hneji. This allows chips to be further easily pushed out toward an outer circumferential area along the chamfers  30 . In addition, the cutting edges  26  can have the increased strength thanks to formation of the chamfers  30 . This effectively prevents occurrence of chipping and breakage resulted from the biting of the chips. Further, the chamfer-side thread portion  24   a  formed on the full thread portion  24  at the distal end is contiguous to the chamfer portion  22 , which has an original complete thread configuration with more than one thread and not more than five threads. In addition, the shank-side thread portion  24   b  formed with the chamfers  30  has an original thread configuration except areas around the cutting edges  26 . Thus, the entire area of the full thread portion  24  can have the excellent guide actions (in lead feed). This can tap the internal threads with high working precision.

TECHNICAL FIELD

The present invention relates to a spiral fluted tap, and moreparticularly, to a technology of preventing occurrence of chipping orbreakage resulted from a biting of chips, especially when a full threadportion is screwed into a threaded bore formed by a chamfer portion.

BACKGROUND ART

There has been a kind of a spiral fluted tap, disclosed in for instancePatent Publication 1, which has a threaded portion formed with cuttingedges extending along spiral flutes so as to divide or to segmentalizeexternal threads. Screwing the threaded portion into a prepared holeallows the cutting edges to cut or to tap internal threads on an innercircumferential surface of the prepared hole, with discharging chipstoward a shank via the spiral flutes. FIG. 4A is a cross-sectional viewshowing one example of such a tapping procedure using the spiral flutedtap. The spiral fluted tap 100 has a threaded portion 102 formed withcutting edges extending along right-hand helix spiral flutes 104, and isrotatably driven clockwise as viewed from a shank 106 for tapping theinternal threads. A worked material 110 is preliminarily formed with aprepared hole 112 into which the spiral fluted tap 100 is screwed at adistal end thereof to tap internal threads on an inner circumferentialsurface of the prepared hole 112.

During such tapping, the chips are discharged via the spiral flutes 104to an outside of the prepared hole 112. However, when a full threadportion is screwed into a threaded hole 114 formed by a chamfer portion,the chips may be bitten to cause chipping of the cutting edges orbreakage of the spiral fluted tap 100. Especially, as the spiral flutedtap dulls due to the use of water-soluble cutting oil and MQL (MinimumQuantity Lubrication) or the like, the chips hardly curled and extendedlengthwise reveals an irregular movement. Thus, the chips are easilybitten to cause a remarkable possibility of the chipping of the cuttingedges or the breakage of the spiral fluted tap.

On the contrary, Patent Publication 2 proposes a technology ofpreventing occurrence of chipping of the cutting edges at distal endsi.e., top ends. As shown in FIG. 4B, the threaded portion 102 includes afull thread portion having a chamfer-side thread portion 122 formed atside of the chamfer portion 120, and a shank-side thread portion 124formed in an area closer to the shank 106. Except for two to fivethreads of the chamfer-side thread portion 122 contiguous to a distalend of the chamfer portion 120, crest portions of the shank-side threadportion 124, positioned radially outside of nearly an effective diameterare cut away (threads being removed). Thus, the occurrence of chippingof the cutting edges at distal ends thereof is prevented.

[Patent Publication 1] Japanese Patent Publication 4-75816

[Patent Publication 2] Japanese Patent Publication 10-118844

DISCLOSURE OF THE INVENTION Subject to be Solved by the Invention

However, in the spiral fluted tap disclosed in Patent Publication 2,only the radially outward portions (outer diametric portion) positionedoutside of the effective diameter are cut away. Therefore, even aftersuch removal, the distal ends of the cutting edges are still sharp toeasily bite the chips and to be easily chipped. Thus, the conventionalspiral fluted tap was not be necessarily satisfied in an adequatemanner.

The present invention has been completed considering with the abovesituations, and has an object to further effectively prevent occurrenceof the chipping of the cutting edges and breakage of the spiral flutedtap resulted from the biting of cutting edges, encountered when screwinga full thread portion into a threaded hole formed by a chamfer portion.

Means for Solving the Subject

For achieving the above object, a first aspect of the present inventionrelates to a spiral fluted tap which includes a threaded portion havingcutting edges formed along spiral flutes formed to divide externalthreads, and being screwed into a prepared hole to cut internal threadsby the cutting edges on an inner circumferential surface of the preparedhole with discharging chips toward a shank via the spiral flutes.

In the spiral fluted tap, (i) cutting faces of the cutting edges of ashank-side thread portion are formed with chamfers retreatingcircumferentially toward crests of the threads, and the shank-sidethread portion is formed on a full thread portion of the thread portion,except for a chamfer-side thread portion having more than one thread andnot more than five threads formed at a distal end contiguous to achamfer portion and is closer to the shank than the chamfer-side threadportion; and (ii) each of the chamfers has a chamfer height Hmen rangingfrom 15% to 100% of a thread height Hneji of the full thread portion.

In a second aspect of the present invention, the chamfers are flatplanar chamfers or arc R (round)-chamfers.

EFFECT OF THE INVENTION

According to the spiral fluted tap, on the shank-side thread portion ofthe full thread portion of the threaded portion formed in the areacloser to the shank, the cutting edges are formed with the chamfers. Thechamfers have the cutting faces each having the chamfer height Hmenfallen within the range of 15% to 100% of the thread height Hneji. Thisallows the chips to be further easily pushed out toward an outercircumferential area i.e., space along the chamfers, respectively. Inaddition, the cutting edges can have the increased strength due toformation of the chamfers. This effectively prevents the occurrence ofchipping of the cutting edges and breakage of the spiral fluted tapcaused by the biting of the chips.

Further, the chamfer-side thread portion, formed on the full threadportion of the threaded portion at the distal end, is contiguous to thechamfer portion, which has an original complete thread configurationwith more than one thread and not more than five threads. In addition,the shank-side thread portion formed with the chamfers has an originalthread configuration except areas around the cutting edges,respectively. Thus, the entire area of the full thread portion can havethe excellent guide action (in lead feed) than that achieved by astructure in which the crests of the threads are cut away in thecylindrical configuration in the areas radially outside the effectivediameter. This can tap the internal threads with further increasedprecision

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1C are views showing a spiral fluted tap of one embodimentaccording to the present invention; FIG. 1A being a front view; FIG. 1Bbeing an enlarged view in cross section taken along a line B-B of FIG.1A; and FIG. 1C being an enlarged view in cross section taken along aline C-C of FIG. 1A.

FIG. 2 is a view illustrating another embodiment in cross sectioncorresponding to that shown in FIG. 1C.

FIGS. 3A and 3B are tables illustrating results on durability testsconducted on test pieces Nos. 1 to 10, involving products of the presentinvention, of ten kinds using two pieces respectively; FIG. 3A being atable illustrating specifications of the test pieces of the ten kinds;and FIG. 3B being a table showing test results on durability tests.

FIGS. 4A and 4B are views illustrating a conventional spiral fluted tap;FIG. 4A being a cross sectional view showing a status under which athread portion is screwed into a prepared hole for tapping; and FIG. 4Bbeing a front view showing the spiral fluted tap a full thread portionis cut away in a cylindrical manner for preventing chips from beingbitten.

EXPLANATION OF REFERENCES

-   10: spiral fluted tap-   16: thread portion-   20: spiral flute-   24: full thread portion-   24 a: chamfer-side thread portion-   24 b: shank-side thread portion-   26: cutting edge-   30: chamfer (flat planar chamfer)-   32: R-chamfer (chamfer)-   O: axis-   Hmen: chamfer height-   Hneji: thread height θ: chamfer angle

BEST MODE FOR CARRYING OUT THE INVENTION

A spiral fluted tap of the present invention allows chips to bedischarged toward a shank. More particularly, the spiral fluted tap isin one style formed cutting edges along right-hand spiral flutes to berotatably driven clockwise as viewed from the shank to perform cuttingwork. In the other style, the spiral fluted tap has cutting edges formedalong left-hand spiral flutes to be rotatably driven counter-clockwiseas viewed from the shank to perform cutting work.

The spiral fluted tap can be made of tool material such as, forinstance, high-speed tool steel (high speed steel) or cemented carbidesteel or the like and possibly applied with hard coating of TiAlN, TiN,TiCN or the like depending on needs. Further, the spiral fluted tap ofthe present invention demonstrates excellent advantageous effectsparticularly when the chips easily extend lengthwise to irregularly movedue to dulling of the spiral fluted tag encountered in the tapping withthe use of water-soluble oil-based cutting agent, MQL (Minimum QuantityLubrication) or oil-less dry machining. However, of course, the spiralfluted tap of the present invention can be used for tapping under wetworking supplied with lubricating oil-based agent at an adequate feedrate.

If a chamfered-side thread portion, having cutting faces not formed withthe chamfer, of a full thread portion has less than one thread, thespiral fluted tap is hardly guided (in lead feed) with increasedprecision. Meanwhile, if the chamfered-side thread portion has more thanfive threads, then, the chamfered-side thread portion will easily bitethe chips, causing the chipping of the cutting edges or breakage of thespiral fluted tap. Therefore, the chamfered-side thread portion needs tohave more than one thread and not more than five (5) threads i.e., fiveor smaller than five.

A chamfer height Hmen of the chamfer refers to a radial dimensionmeasured based on a distal end (outer circumferential edge) of eachcutting edge before the distal ends i.e., radially top ends beingchamfered. A thread height Hneji of the full thread portion refers to aradial dimension of a thread between a root and top thereof, and it isparticularly represented in terms of “(Tap Outer Diameter−Tap RootDiameter)/2”. If the chamfer height Hmen is less than 15% of the threadheight Hneji, the chamfer can not suppress the biting action of thechips, and can not render adequate improved strength of the cuttingedges. In contrast, if the chamfer height Hmen exceeds 100% of thethread height Hneji, then, a gap is created between the prepared hole(threaded hole) and the spiral fluted tap with an adverse effect ofeasily biting the chips. Therefore, the chamfer height Hmen needs tofall in a range between 15% and 100% of the thread height Hneji. Thechamfer height Hmen may be fixed i.e., constant in value but may bepossibly varied in an axial direction within a predetermined range in acontinuous or stepwise manner. Alternatively, the chamfer height Hmenmay have differing dimensions different for plural cutting edges,respectively.

Chamfered shapes may have flat planar chamfer, or arc R-chamfer. Theflat planar chamfer will be described below in detail with reference toa case wherein each flat planar chamfer has a chamfer angle θ angledwith respect to a base line L connecting between a radial distal endi.e., top end (outer circumferential edge) of the cutting edge beforethe chamfering and a tapping axis O, in a cross section perpendicular toeach cutting edge. If the chamfer angle θ is too small, then the chamfercan not render the suppressing action of the biting of the chips, andcan improve the strength of the cutting edge by the chamfer. Thus, thechamfer angle θ may preferably be selected to fall in a value of, forinstance, 20° or more.

On the contrary, if the chamfer angle θ is too large, then, the spiralfluted tap has a decreased angle between the chamfer and the cuttingface, easily catching the chips with increased likelihood. Thus, thechamfer angle θ may preferably be selected to fall in a value of, forinstance, 60° or less. Although the chamfer angle θ may have a fixedvalue, it may be possibly varied within a predetermined range along anaxial direction in a continuous or stepwise manner. In an alternative,the chamfer angle θ may have differing dimensions different for pluralcutting edges, respectively.

The R-chamfer is formed in a circular arc configuration with a radiusbeing nearly fixed such that the R-chamfer is smoothly connected to thecutting face and the crest of the thread, in a cross sectionperpendicular to, for instance, the cutting edge. However, the R-chamfermay have a circular arc configuration with the radius of the curvaturevarying continuously due to a convenience of working.

Threads of the full thread portion may preferably have thread reliefsi.e., reliefs such as eccentric reliefs or the like, respectively. In analternative, threads of a fixed diametrical dimension with no reliefscan be adopted. That is, it may suffice for the spiral fluted tap of thepresent invention to have the chamfers formed on the cutting faces ofthe cutting edges of the shank-side thread portion of the full threadportion, and for the thread reliefs to take a variety of designsincluding presence/absence of the thread reliefs. For instance, areas ofthe threads in close proximity to the crests can be cut away intocylindrical configurations.

A flute angle of the spiral flute provided on the threaded portion maypreferably be selected to range from approximately, for instance, 15° to50°. Moreover, the number of teeth of the cutting edges is appropriatelyvaried to have, for instance, about 2 to 6 cutting edges depending onwork material to be cut or a tapping size.

Embodiment

Hereunder, embodiments of the present invention will be described belowin detail with reference to the accompanying drawings. FIGS. 1A to 1Care views showing a spiral fluted tap of one embodiment according to thepresent invention; FIG. 1A being a front view; FIG. 1B being an enlargedview in cross section taken along a line B-B of FIG. 1A; and FIG. 1Cbeing an enlarged view in cross section taken along a line C-C of FIG.1A.

A spiral fluted tap 10 includes a shank 12, a neck portion 14 and athreaded portion 16, which are integrally formed on a common axis O insuch an order. The threaded portion 16 has external threads formed ingroove profiles corresponding to internal threads to be cut, and threespiral flutes 20 formed so to divide the external threads. The threadedportion 16 includes a chamfer portion 22 formed at an axial distal endthereof with threads 18 of the external threads being removed in theaxial direction in a tapered shape, and a full thread portion 24contiguous to the chamfer portion 22 and having the full threads 18.Cutting edges 26 are formed at ridgelines between the threaded portion16 and the spiral flutes 20.

The spiral flutes 20 are right-hand helixes each of which has a helixangle falling within a range of, for instance, 15° to 50° to lie at avalue of approximately, for instance, 40°. In use, the spiral fluted tap10 is rotatably driven clockwise as viewed from the shank 12 so that adistal end is screwed into, for instance, the prepared hole 112 of thework material 110 shown in FIG. 4A. Thus, the internal threads are cuton an inner circumferential surface of the prepared hole 112 with thespiral flutes 20 permitting chips to be discharged toward the shank 12.

The full thread portion 24 has chamfers i.e., chamfered portions 30.Each of these chamfers 30 is formed on a cutting face i.e., rake face(forming part of each spiral flute 20) of the cutting edge 26 of ashank-side thread portion 24 b formed in an area closer to the shank 12,except for a chamfer-side thread portion 24 a. The chamfer-side threadportion 24 a is formed on the full thread portion 24 in an end portionthereof to be contiguous to the chamfer portion 22 and has more than onethreads and not more than five threads. The chamfers 30 are retreatedcircumferentially (to heel side) toward the crests i.e., outercircumferences of the threads 18. That is, the chamfers 30 are inclinedcircumferentially (to heel side) as distance from the axis increases.FIG. 1B is a cross-sectional view of the chamfer-side thread portion 24a which has no chamfers 30. FIG. 1C is a cross-sectional view of theshank-side thread portion 24 b in which the chamfers 30 are provided.The chamfer 30 has a chamfer height Hmen determined to lie in a value ofabout, for instance, 50% falling in a value ranging from 15% to 100% ofa thread height Hneji of the full thread portion 24. The chamfer heightHmen represents a radial dimension of the chamfer measured based on adistal end i.e., radially top end (outer circumferential edge) of eachcutting edge 26 prior to the formation of each chamfer. The threadheight Hneji represents a radial dimension of the thread 18 from a rootto a crest that is concretely expressed by the relationship (Tap OuterDiameter−Tap Root Diameter)/2.

The chamfer 30 is a flat planar chamfer having a chamfer angle θ, angledwith respect to a base line L connecting between the distal end (outercircumferential edge) of the cutting edge 26 prior to the chamferformation and a tap axis O, which lies in a value of approximately, forinstance, 45° within a range of 20° to 60°. The chamfer angle θ isindicated in a cross section perpendicular to the axis O in FIG. 1C.Strictly speaking, however, the chamfer angle θ represents an angle incross section perpendicular to the cutting edge 26 formed along eachspiral flute 20 and falls in a value ranging from 20° to 60°.

In the illustrated embodiment, both the chamfer height Hmen and thechamfer angle θ are set in fixed dimensions at fixed angles over anentire area of the shank-side thread portion 24 b. In the illustratedembodiment, further, the spiral fluted tap 10 is made of high-speed toolsteel (powdered high-speed steel) with the threaded portion 16 having ahard coating of TiCN. Although each of the threads 18 of the full threadportion 24 in FIGS. 1B and 1C each has a profile extending to a heelwith a fixed radial dimension with no chamfer relief, the thread 18 mayhave a relief such as an eccentric thread relief or the like dependingon needs. The threads 18 of the chamfer portion 22 are formed withpredetermined reliefs, respectively.

According to the spiral fluted tap 10 of the present invention, of thefull thread portion 24 of the threaded portion 16, the cutting edges 26of the shank-side thread portion 24 b formed in the area closer to theshank 12 are formed with the chamfers 30. The chamfer 30 have thecutting faces each having the chamfer height Hmen fallen within therange of 15% to 100% of the thread height Hneji. This allows the chipsto be further easily pushed out toward an outer circumferential areai.e., space along the chamfers 30, respectively. In addition, thecutting edges 26 can have the increased strength thanks to formation ofthe chamfers 30. This effectively prevents the occurrence of chipping ofthe cutting edges and breakage of the spiral fluted tap caused by thebiting of the chips. Thus, the spiral fluted tap has the increaseddurability (operating life).

Further, of the full thread portion 24 of the threaded portion 16, thechamfer-side thread portion 24 a formed on the full thread portion 24 atthe axial distal end thereof is contiguous to the chamfer portion 22,which has an original complete thread configuration with more than onethread and not more than five threads. In addition, the shank-sidethread portion 24 b formed with the chamfers 30 has an original threadconfiguration except areas around the cutting edges 26, respectively.Thus, the entire area of the full thread portion 24 can have the moreexcellent guide actions (in lead feed) than that achieved by a structurein which the crests of the threads are cut away in the cylindricalconfiguration in the areas radially outside the effective diameter. Thiscan tap the internal threads with further increased precision.

Furthermore, in the present embodiment, the chamfer 30 formed in theflat planar chamfer has the chamfer angle θ falling in a value rangingfrom 20° to 60°. The chamfer angle θ allows the chamfers 30 toappropriately obtain the suppression action of the biting of the chips,and to improve strength of the cutting edges. Thus, the spiral flutedtap has the increased durability.

While in the illustrated embodiment, the chamfers 30 are formed in theflat planar chamfers, respectively, R-chamfers 32 i.e., round chamfer 32may be provided as shown in FIG. 2. The R-chamfers 32 are formed on thespiral flutes 20 in cross section perpendicular to the cutting edge 26,respectively, to be smoothly contiguous to the cutting faces (spiralflutes 20) and the crests of the threads 18. Each of the R-chamfers 32each has a circular arc with, for instance, a nearly fixed curvature.

FIGS. 3A and 3B are tables illustrating test results on ten kinds oftest pieces Nos. 1-10 involving the test pieces of the presentinvention, each prepared in two pieces, and respective test pieces wereused for tapping under a cutting condition listed below to checkdurability thereof. FIG. 3A is a table illustrating specifications ofthe test pieces of ten kinds. FIG. 3B is a table showing test results ofthe test pieces with durability being checked in terms of thepresence/absence of the chipping or the breakage.

(Cutting Condition)

Size: M8×1.25

Worked Material: SUS304

Cutting Speed: 8 m/min

Shape of Prepared Hole: Through-hole with φ6.8×25 mm

Effective Length of Threads: 16 mm (two times that of tool diameter)

Cutting Fluid Water-Soluble Cutting Oil

Machine used: Transverse type Machining Center

The test pieces Nos. 1-10 have the same fundamental shapes as that ofthe spiral fluted tap 10 of the present embodiment. In FIG. 3A,underlined parts indicate items different from the present invention.That is, the test pieces No. 1 represent the conventional products inwhich the chamfers 30 or 32 are not provided. The test pieces No. 2represent the conventional products disclosed in Patent Publication 2.Each of them includes the chamfer-side thread portion 24 a having fourthreads, and the shank-side thread portion 24 b having the crests beingcut away in the cylindrical shape at areas radially exceeding theeffective diameter. The test pieces No. 3 represent comparison productseach including the chamfer-side thread portion 24 a having the fourthreads and having the chamfer of the chamfer angle θ=45°. However, thechamfer height Hmen with 10% of a thread height Hneji is too small.

All the test pieces Nos. 4-8 represent products of the presentinvention, each formed with the chamfer-side thread portion 24 a having1.5 threads or four threads, each having the flat chamfers with thechamfer angle θ of 30° or 45° or the R-chamfers formed in the circulararc configurations, and each of the chamfer heights Hmen has value of20%, 50% and 100% the thread height Hneji, respectively. The test piecesNo. 9 represent comparison products, each formed with the chamfer-sidethread portion 24 a having four threads, each having the chamfers with achamfer angle θ=45°, and a chamfer height Hmen is too large with a value1.2 times the thread height Hneji. The test pieces No. 10 representcomparison products, each having a chamfer angle θ=45°, and a chamferheight Hmen is 50% of the thread height Hneji. However, the chamfer-sidethread portion 24 a has too many number of threads with six threads.

As will be apparent from the test results shown in FIG. 3B, all the testpiece Nos. 4-8 of the present invention can tap more than 900 holes.Particularly, the test pieces Nos. 5-7 still remained operative tosuccessively tap holes even after they tapped 1000 holes. On thecontrary, one of the test pieces No. 1 of the conventional art isdamaged merely upon tapping 56th holes. One of the test pieces No. 2,having the effective diametric portion cut away in the cylindricalshape, is damaged upon tapping 598th holes. Although this test piece No.2 revealed further remarkably increased durability than those of thetest pieces No. 1, such a result was nearly half that of durability ofthe products (test pieces Nos. 5-8) of the present invention.

Further, one of the comparison products of the test pieces No. 3 isdamaged upon tapping 108th holes, and can not improve the durabilitywith the provision of the chamfers 30. Furthermore, ones of thecomparison products of the test pieces Nos. 9 and 10 can tap 608 and 705holes, respectively. Although these test pieces had effects of improvingdurability at certain degrees, they revealed no remarkable difference ascompared to the results of the comparison products of the test piecesNo. 2.

In the foregoing, while the present invention has been described abovewith reference to the accompanying drawings, it is intended that theembodiment described be considered only as illustrative of the presentinvention and that the present invention may be implemented in variousmodifications and improvements based on knowledge of those skilled inthe art.

INDUSTRIAL APPLICABILITY

In the spiral fluted tap, on the full thread portion of the threadedportion, the cutting edges of the shank-side thread portion formed inthe area closer to the shank are formed with the chamfers. The chamfershave the cutting faces each having the chamfer height Hmen fallen withinthe range of 15% to 100% of the thread height Hneji. This allows thechips to be further easily pushed out toward an outer circumferentialarea along the chamfers. In addition, the cutting edges can have theincreased strength thanks to formation of the chamfers. This effectivelyprevents the occurrence of chipping of the cutting edges and breakage ofthe spiral fluted tap caused by the biting of the chips. Thus, thespiral fluted tap can be preferably used for the tapping.

1. A spiral fluted tap which includes a threaded portion having cuttingedges formed along spiral flutes formed to divide external threads, andbeing screwed into a prepared hole to cut internal threads by thecutting edges on an inner circumferential surface of the prepared holewith discharging chips toward a shank via the spiral flutes, comprising:cutting faces of the cutting edges of a shank-side thread portion beingformed with chamfers retreating circumferentially toward crests of thethreads, and the shank-side thread portion being formed on a full threadportion of the thread portion, except for a chamfer side thread portionhaving more than one thread and not more than five threads formed at adistal end contiguous to a chamfer portion and being closer to the shankthan the chamfer-side thread portion; and each of the chamfers having aheight Hmen ranging from 15% to 100% of a thread height Hneji of thefull thread portion.
 2. The spiral fluted tap according to claim 1,wherein the chamfers are flat planar chamfers or arc R-chamfers.
 3. Thespiral fluted tap according to claim 1, wherein the chamfers are flatplanar chamfers formed such that a chamfer angle ranges from 20° to 60°in a cross section perpendicular to the cutting edges formed along thespiral flutes.
 4. The spiral fluted tap according to claim 1, wherein aflute angle of the spiral flutes ranges from 15° to 50°.
 5. The spiralfluted tap according to claim 1, wherein the number of cutting edgesranges from 2 to 6.